On the derivation of half angle formula TaNx / 2 = under positive and negative root sign (1-cosx) / (1 + cosx) = (1-cosx) / SiNx Why is there no positive or negative in the last step

On the derivation of half angle formula TaNx / 2 = under positive and negative root sign (1-cosx) / (1 + cosx) = (1-cosx) / SiNx Why is there no positive or negative in the last step

Because the sign of sine function is consistent with its sign, and the sign of 1 and cosine is not limited to zero